The monitoring of flow of goods is becoming increasingly important, first of all because the volume of transported goods is constantly increasing worldwide, and secondly because it is essential to deliver goods, especially industrial goods, to their destinations precisely in time for further processing according to the so-called just-in-time concepts. Because of the increasing complexity and increasing volume of the flow of goods, the logistic monitoring thereof is becoming increasingly important.
FIG. 1 shows a prior art transport monitoring system, where goods are transported from a warehouse A to a warehouse B. The goods W are provided with so-called tags T for transport monitoring purposes. Tags are identification elements which include a carrier, such as an article label, and a small transponder chip. RFID (radio frequency identification) chips are known, a distinction being made between passive, semi-active and active tags. The tags serve to identify the goods on which they are provided. A reader unit, or reader, includes a receiver unit for transmitting and receiving electromagnetic waves. The emitted waves are received by a coil provided in the tags. Tags receive, from the transmitter/receiver unit of the reader, a signal pulse to send an individual response signal back to the reader.
Passive tags have no integral power supply, but absorb the energy of the emitted pulse and use the absorbed energy to generate the response signal. Passive tags, by nature, have a relatively small range.
Semi-active tags have an integral power supply, one part of the energy required for the response being supplied by the integral power supply, and another part being obtained from the signal received from the reader. The range of semi-active tags is slightly larger than that of passive tags.
Active tags also have an integral power supply, the energy for the response signal for identifying the goods being completely obtained from the integral power supply.
Active tags are irradiated by the reader with relatively low transmitted power, while passive tags are irradiated with relatively high transmitted power because they have to obtain therefrom the energy for generating the response signal. Passive tags have the advantage of not requiring an integral power supply. However, they need to be irradiated with relatively high power. On the other hand, active tags have the advantage of having to be irradiated only with relatively low transmitted power. However, there is a risk that the power supply of the active tags may fail after a certain period of time.
In the transport monitoring system illustrated in FIG. 1, the goods to be transported W are loaded from a warehouse A into a transport device, for example into a truck, through a reader unit LA. Reader unit LA identifies the goods loaded into the truck by the tags T attached to goods W. Reader unit LA has connected thereto an evaluation unit which, for example, updates the inventory list of warehouse A. The transport device; i.e., the truck, takes the goods provided with tags T to a destination warehouse B. The goods are unloaded from the truck, passed through a reader unit LB, and stored in destination warehouse B. Reader unit LB identifies the goods received into warehouse B by the tags T attached to goods W. An evaluation unit connected to reader unit LB updates the inventory of warehouse B.
The transport monitoring system shown in FIG. 1 has several disadvantages. There is a risk that goods may indeed be passed through reader unit LA, but not actually get into the truck or transport device. Goods may intentionally or unintentionally pass reader unit LA without being loaded into the truck. For example, goods W may be erroneously loaded into the wrong truck and taken to a different warehouse. Moreover, there is no monitoring of the goods while in the truck and on the transport path between the two warehouses A, B.
German Patent Application DE 19 844 631 A1 proposes a system for monitoring, controlling, tracking and handling objects, as illustrated in FIG. 2. The transport device described in DE 19 844 631 A1, which may be a truck, includes a write/read device for reading tags T, which are attached to goods W within the transport device. The reader unit, or reader, emits interrogation signals, i.e., electromagnetic signals, into the cargo space of the truck and receives identification data signals from the transponders located in the cargo space. An evaluation unit attached to the reader unit, or reader, evaluates the received identification data signals, thereby monitoring, for example, whether all loaded goods are still in the cargo space. The mobile data carriers, or tags, attached to the goods send identification data and object-specific data to the reader unit. Moreover, the tags attached to the goods send further data, such as data indicative of the temperature in the shipping container. For example, if the measured temperature exceeds or falls below a threshold value, a warning will be issued to the truck driver, who will initiate the necessary countermeasures. The transport monitoring system shown in FIG. 1, it has considerable disadvantages.
If goods are removed from the truck shown in prior art FIG. 2, for example by theft, the goods, and the tags attached thereto, get out of the transmission range of the reader, or reader unit. Therefore, in order to detect such shrinkage of goods, the reader unit must emit an interrogation signal into the cargo space of the truck, either constantly or at regular intervals (for example, every five minutes). If there is a suspicion that goods have been stolen from the cargo space, the write/read device can also be activated by the driver in order to read the tags.
A disadvantage of the transport monitoring system described in DE 19 844 631 A1 is that the use of active tags for monitoring the goods is unsafe when the interrogation signal is emitted periodically or constantly. Due to the periodic emission of the interrogation signal, a load is placed on the power supply or battery of the active tags on a regular basis, so that the battery of the active tags will gradually discharge. Once the battery of the tags is empty, the tags are unable to send an identification data signal back to the reader, which leads to unwanted, incorrect messages. If the intervals between the interrogation signals are increased, for example, to a period of 10 minutes, there is a risk of goods being stolen from the transport device in the meantime. An increase in the time period for emitting the interrogation signal does, in fact, extend the life of the active tags, but loss or theft of goods is usually detected later in time.
Another disadvantage of the conventional transport monitoring system illustrated in FIG. 2 is that the system is not secure against tapping. When write/read units emit interrogation signals into the transport device, the tags attached to the goods respond by sending identification data signals back to the reader unit. Since the identification data signals are also radiated outside the transport device, for example, to a vehicle traveling behind the truck, the emitted identification data signals enable third parties to easily identify the goods transported in the truck. Thus, third parties may find out whether it is worthwhile to steal the goods. Thus, due to the lack of security against tapping, secret transport of certain goods, for example, in a military context, cannot be reliably prevented from being noticed by third parties.
A further disadvantage of the transport device shown in FIG. 2 is that the interrogation signal emitted by the write/read unit and the identification data signals returned by the tags cause problems in terms of electromagnetic compatibility. Interrogation signals and the returned identification data signals may interfere with other electronic systems in the transport device. If the transport device is, for example, an aircraft, the periodically emitted interrogation signal and the returned identification data signals may interfere with the sensitive electronics located therein and pose a safety risk.
It is yet another disadvantage of the transport device shown in FIG. 2 that the transport monitoring system is a local system in which the driver of the transport device responds to error messages. If, for example, goods are stolen from the transport device with the aid of the driver, this cannot be detected immediately.